Injection molding is a manufacturing process for producing molded parts or molded products from materials including thermoplastic and thermosetting plastic materials. The molding process typically involves feeding a material to be molded into a heated chamber for melting and then forced under pressure via flow paths into a mold cavity where the material cools and hardens to form a final molded part. The mold cavity is then opened and the final molded part is ejected from the mold cavity.
Conventional injection molding architecture comprises of a stationary mold plate and a movable mold plate, housing a mold cavity to form a molded article in between the plates. The mold plates are held together by a clamping arrangement during a molding cycle. The molded part is ejected from the cavity space of movable mold plate by an ejection mechanism, which involves a plurality of ejector pins sliding in unison through the movable plate in order to contact the surface of the molded part and dislodge the molded part. The ejector pins are actuated by an ejector plate for enabling the pins to slide through the mold plate and alternatively, backward movement of the mold plate which comprises respective channels for slides over the ejector pins fixed to a support plate. During a typical ejection process, the ejector plate is moved forward thereby actuating the pins to simultaneously slide through the mold plate in order to push the molded article off the mold cavity.
However when the molded article does not typically fully harden during the cooling phase of the injection molding cycle, then ejection time has to be delayed until that article turns hard enough to be ejected. Another approach is to employ alternative methods of ejection such as manually pulling the molded part out of the mold or stripping the molded part off a mold cavity using an automated process.
For example, in the case of molded pet treats, if the pet treat dough or mix is not completely solidified at the time of mold opening then subsequent ejection process would damage the product. The damage occurs when all the ejector pins simultaneously press on the surface of molded pet treat in an attempt to eject eventually results in distortion of pet treat due to the pins passing through the non-hardened dough or partial ejection of the molded pet treat from the mold cavity.
Different functional designs of ejection pins adapted to eject the molded material from a mold are known in the art including: single unitary type pins with base portion fixed to the ejector plate; ejector pins adapted to slide through a movable mold plate, wherein the ejector pins are actuated by the movement of ejector plate; and ejector pins with base end flange portions linked to a cylinder rod of an air cylinder, which is fixed to the ejector plate.
Ejection of the molded material from a mold cavity is also carried out by employing angular ejector pins in an injection mold for ejecting a plastic article molded in the injection mold. While mold opening, the angular ejector pin moving at an angle ejects the plastic article out from mold cavities of the injection mold.
Ejection mechanism or ejector devices of injection molding machines known in the art poses limitations such as synchronous movement of unitary ejector pins pushing the surface of a molded material may result in damaging at least parts of the molded material, especially in a non-solidified state during ejection. In another case, a part of the molded material may stick to the cavity thus leading to incomplete ejection and even distorted final molded article at times. Further limitation includes additional wait time for allowing solidification or cooling of the mold material before mold opening which results in delayed molding process.
U.S. Pat. No. 6,491,512 B2 shows a two stage ejection system for an injection mold. U.S. Pat. No. 7,435,079 B2 discloses an angular ejector pin mechanism for ejecting plastic articles from an injection mold. U.S. Pat. No. 8,393,884 B2 shows an ejector device of an injection molding machine. US patent publication number 20130251837 shows a type of injection molding machine. US patent publication number 20060172037 shows ejection of molded part using a decelerated ejector pin.
Accordingly, there exists a need for an efficient method for ejecting a molded part or product from a mold cavity without damaging the molded part or product in an unsolidified or uncured state.